The Prospects for Calendar Reform

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[edit] Why is calendar reform desirable?

Before considering the prospects for calendar reform we should be clear about why reform of the calendar is desirable.

Calendar reform means improving, or replacing, the Common Era Calendar which, since early in the 20th Century, has been the standard calendar in use in most countries in the world.

Reasons for retaining this calendar are:

1. The calendar year stays in sync fairly well with the seasonal year. More exactly, the vernal equinox always occurs during a 51-hour period spread over March 19, 20 and 21.
2. Everyone is familiar with it.
3. The rules of the calendar are already embedded in innumerable computer programs.
4. The calendar is an integral part of the vernacular of many cultures.
5. It maintains an uninterrupted seven-day week, which is important to religious groups.
6. It may be difficult to promulgate changes to the calendar because all countries that use it would need to agree to make a change. The Gregorian calendar took nearly 350 years to be adopted by all countries that previously used the Julian calendar.

Reasons for modifying or replacing this calendar are:

1. The structure of the months is irregular, with month lengths ranging arbitrarily from 28 days to 31 days.
2. The leap year rule is hard for many people to understand: "An extra day is added at the end of the second month every four years, except in years whose number is divisible by 100 except in years whose number is divisible by 400."
3. The conventional 7‑day‑week cycle does not fit exactly into a Common Era year (there are always one or two days left over). This means that it is difficult to know which day of the week a CE date falls on.
4. The irregularity of the structure of the CE Calendar makes it difficult to formulate schedules of events occurring on certain days of the week which can be re‑used from year to year.
5. That irregularity also makes it very difficult to design schedules which can be used in any quarter (of three months), term (of four months) or semester (of six months).
6. Despite the existence of a proposed standard way of writing CE dates (the ISO 8601 date format) such dates are currently expressed mainly either as month-day-year (in the U.S.) or day-month-year (in Europe and most of the rest of the world). This creates major confusion for people in one part of the world reading dates written by and for people in another part of the world.
7. The months of the CE Calendar, although called "months", have no relation to the lunar cycles. The sequence of months and the sequence of lunations are completely unrelated, and a new moon or a full moon can occur on any day of the CE month.
8. The leap year rules cause the timing of the equinoxes and solstices to vary by about 51 hours, which can be reduced if alternative leap year rules were adopted.
9. The intercalary day is inserted at the end of the second month instead of at the end of the year, which adds complexity to various date calculations. In particular, the number of days between a particular date in January or February and a particular date after the end of February is not constant.

Can the CE Calendar be "tweaked" so as to overcome these flaws? If not then calendar reform means the replacement (by some means) of the CE Calendar by another, in which case a candidate for replacement should preserve (or even improve on) the CE Calendar's accord with the seasonal year while having, as far as possible, none of the defects mentioned above.

[edit] What kind of calendar?

Calendars are social constructs, since they do not occur outside of human (or some kind of) society. There are two fundamental views of what a calendar is (or should be). One is the view that a calendar formalizes a relation between humans and cycles which occur in nature. The other is the view that a calendar is a means for organizing and coordinating social activities.

Since the seasonal year has always been of primary importance for human economic activities, most calendars have the seasonal year as a unit, in accordance with the view that a calendar should relate to natural cycles. Such calendars are called solar calendars. There are some exceptions, such as (a) the Islamic Calendar, which has a year of twelve lunar months, about eleven days shorter than the seasonal year and (b) the 260-day cycle of the Maya tzolkin.

The lunar cycle (which is approximately 29½ days) has also historically been important to humans, and many calendars (such as the Islamic) have as a subdivision of the year the unit of the month, sometimes regarded as the period from one new moon to the next.

But a calendar which stays in sync with the lunar cycles, that is, a lunar calendar, tends not to be easy to use for organizing social activities which occur at intervals of less than 29 days. Thus the view of calendars as primarily devices for scheduling social events (other than those occurring at new moon and full moon) tends not to attribute much importance to lunar cycles.

If it is accepted that a new calendar should be a solar calendar then the question arises as to whether it should also be a lunar calendar, and thus a lunisolar calendar. Or whether it is more important to have a calendar which facilitates scheduling (so that, for example, schedules may be re-used from year to year).

If a calendar has a year which is divided into months, then a second fundamental question is whether there should be a unit of time intermediate between month and day, and if so, of how many days should it consist?

Traditionally (in societies using the CE Calendar or its historical predecessor, the Julian Calendar) this unit has been the 7-day week. This unit is especially useful for scheduling human activities, but it does not relate well to the length of the lunar cycle (29½ days).

Perhaps not just one new calendar is needed, but two: One which is a reflection of natural cycles (in particular, the Moon) and one which is mainly intended for scheduling purposes. This has a precedent in that some societies have had a 'sacred' calendar and a 'civil' calendar (for example, the Maya tzolkin and haab calendars). Also some contemporary societies use more than one calendar simultaneously, e.g., in China the CE Calendar is used for business purposes but the traditional Chinese Lunar Calendar remains in use. Thus calendar reform should not necessarily be seen as the replacement of the CE calendar with just one new calendar.

[edit] Transitional considerations

Since the use of the Common Era Calendar is so widespread and embedded so deeply in Western society, and since there is no calendrical authority to mandate use of one calendar rather than another, a change from the CE Calendar to a better successor is likely to be a gradual process. Thus any proposal for calendar reform must consider how the transition from the old to the new is to be managed.

Some things to be considered are:

• Do the old and the new calendars have anything in common (such as use of the 7-day week with the same day names) which will ease the transition?
• What, if anything, about the new calendar will motivate people to use it?
• Will people believe that in adopting the new calendar something is lost by abandoning the old, thereby making them reluctant to change?
• How easy will it be for people to convert dates in the old calendar to dates in the new (and vice-versa). Can this be done with (at most) pencil and paper, or can it only be done by complex calculations requiring the use of a calculating device?
• What is to be done about all the software which currently is written to handle dates in the old calendar? How easy will it be for programmers to modify the software to handle dates in the new calendar?
• Are there clear algorithms provided for the new calendar which allow conversion between dates and Julian day numbers, thus facilitating conversion between dates in the new calendar and dates in any other?
• For how long should the old and the new calendars be maintained concurrently before the old is definitely seen to be a thing of the past?